Photolithography techniques are used in processes for producing semiconductors, etc., and for example, a process for producing semiconductor circuits includes steps of forming patterns of resist (resist pattern).
When the resist layer formed on a substrate is irradiated with exposure light, in addition to the light incident on the resist layer, the light reflected from the substrate surface, and the light which is generated from such a reflected light reflected from the surface of the resist layer again will interfere each other. As a result, standing waves are generated. Such standing waves may cause dimensional changes and collapses of the shape of the resist pattern, etc.
Further, there may be the case that fine resist patterns are to be formed on the surface having differences in level. In such a case, the dimensional changes and collapses of the shape due to the standing waves (standing wave effect) tend to be large.
Heretofore, as methods for suppressing the standing wave effect, a method of incorporating a light absorbing agent in the resist material, a method of providing an antireflection coating layer on the top surface of resist layer (TARC method), a method of providing an antireflection coating layer on the lower surface of resist layer (BARC method), etc. have been proposed.
The TARC method is a method of providing, on the resist layer, an antireflection coating layer having a lower refractive index than the resist layer, whereby the lower the refractive index of the antireflection coating layer is, the higher the obtainable antireflection effect is.
Patent Document 1 discloses, as the antireflection coating composition to be used in the TARC method, a composition having a polymer having —(CF2—CFOCF2CF2COOH)— units dissolved in a mixed solvent which consists of water and methanol.
In general, it is known that the ideal refractive index of the antireflection coating layer is the square root (√n) of the refractive index n of the photoresist layer for obtaining excellent antireflection effect in the TARC method, and the ideal coating layer thickness is odd number of multiple of λ/4m (λ is the wavelength of radial rays, and m is the refractive index of the antireflection coating layer) (Patent Document 2, paragraph.